Articles of athletic footwear often include two primary elements, an upper and a sole structure. The upper provides a comfortable covering for the foot and securely positions the foot with respect to the sole structure. The sole structure is secured to a lower portion of the upper (for example, through adhesive bonding) and is generally positioned between the foot and the ground. In addition to attenuating ground reaction forces (that is, providing cushioning) during walking, running, and other ambulatory activities, the sole structure may influence foot motions (for example, by resisting pronation), impart stability, and provide traction. Accordingly, the upper and the sole structure operate cooperatively to provide a comfortable structure that is suited for a wide variety of athletic activities.
The upper is often formed from a plurality of material elements (for example, textiles, polymer sheets, foam layers, leather, and/or synthetic leather) that are stitched and/or adhesively bonded together to form a void on the interior of the footwear for receiving a foot. More particularly, the upper forms a structure that extends over instep and toe areas of the foot, along medial and lateral sides of the foot, and around a heel area of the foot. The upper may also incorporate a lacing system to adjust fit of the footwear, as well as permitting entry and removal of the foot from the void within the upper. In addition, the upper may include a tongue that extends under the lacing system to enhance adjustability and comfort of the footwear. Further, the upper may incorporate a heel counter to provide stability, rigidity, and support to the heel and ankle portion of the foot.
The sole structure may include one or more components. For example, the sole structure may include a ground-contacting sole component. The ground-contacting sole component may be fashioned from a durable and wear-resistant material (such as rubber or plastic), and may include ground-engaging members, tread patterns, and/or texturing to provide traction.
In addition, in some embodiments, the sole structure may include a midsole and/or a sockliner. The midsole, if included, may be secured to a lower surface of the upper and forms a middle portion of the sole structure. Many midsole configurations are primarily formed from a resilient polymer foam material, such as polyurethane or ethylvinylacetate, that extends throughout the length and width of the footwear. The midsole may also incorporate fluid-filled chambers, plates, moderators, or other elements that further attenuate forces, influence the motions of the foot, or impart stability, for example. The sockliner is a thin, compressible member located within the upper and positioned to extend under a lower surface of the foot to enhance footwear comfort.
The footwear components discussed above may be assembled together using various methods, including, for example, stitching, adhesives, welding, and other joining techniques. Articles of footwear may be assembled, at least in part, on a structure called a “last.” A last is a form having the general shape of a human foot. During manufacturing, an article of footwear may be assembled around a last, in order to create a shoe with the desired shape. For example, upper materials/panels may be assembled, or otherwise placed, on a last. Then other components, such as midsole components and/or ground-contacting components may be attached to the upper, while fitted on the last. A last is typically not shaped like any particular type of foot, but rather is formed having a shape wherein the dimensions are averages of many different foot types, in order to produce a shoe that fits a variety of foot types.
When joining footwear components using welds and/or adhesives, heat may be applied to select portions of the footwear components. Therefore, systems have been developed to provide heat to certain portions of footwear components. There are various ways in which the heat may be applied. The heat may activate adhesive applied to portions of the footwear components, thereby joining the components. In some cases, the heat may be applied to effectively melt portions of footwear components (for example plastics) in order to join the components together. In other techniques, heat may be applied to footwear components in order to shape the components. For example, such techniques may involve heating a footwear component while a form (such as a last or an actual human foot) is pressed against it, in order to mold the component to the form.
Systems have been developed that apply heat using electrical heating elements. Some systems incorporate electrical heating elements into the last. Once heated by the electrical heating elements, the last conductively transmits heat to components of footwear fitted on the last or otherwise pressed against it. Such systems heat adhesives applied to the footwear components in order to join the components to one another.
In other systems, irradiative heating may be applied to join components of footwear. For example, microwave or infrared irradiation may be applied to footwear components from external sources to apply heat for shaping or joining footwear components. Some systems have been developed that apply microwave or infrared irradiation to heat adhesives in order to join footwear components.